with us. nbc's chief correspondent. what are you hearing at the pentagon. >> officials knew this was coming although they didn't know the exact timing. this one has set off alarm bells, particularly because of the size of the blast. we're not relying on north korea claims here. south korea's seismic readings on the blast said it was somewhere about 6 or 7 kilotons, which could make it anywhere from 3 to 6 times more powerful than any previous weapon they set off before. north korea did claim they did this with a much smaller warhead, which would indicate they could be making progress miniaturizing a missile that could be launched at the united states. that's north korea and nobody is taking that seriously at this point and quite frankly, that's impossible to prove. within minutes, it seemed, after the blast was reported, the white house responded and president obama called it a highly provocative act that undermines regional stability and threatens ultimately u.s. national security. the president said it demands swift and credible action by the international community. that'